For conventional all-air-conditioning systems, the indoor load in the air conditioned area is fully borne by the heated or cooled air. To bear the indoor load, most conventional schemes employ condensation dehumidification way to process the air; however, the temperature of cold source required for cooling is actually apparently higher than the temperature of cold source required for dehumidification. Hence, it is difficult to meet the requirement for simultaneous change of indoor air temperature and humidity in the building by such an approach. In addition, since the fresh air handling unit in the system usually employs cooling coil pipes for dehumidification, the surfaces of the coil pipes always carry water. During the off-time of the system (at night or on non-working days), the surface temperature of the coil pipes increases, and the coil pipe surfaces contact with the air, providing nutritional conditions for reproduction of microorganisms and contaminating the fresh air.
Conventional single stage single-effect lithium bromide absorption refrigeration systems have favorable performance for air conditioning, and the temperature range of the low-grade heat source required for such a system is 90˜120° C. If the temperature is lower than the lowest generation temperature, the conventional single-effect absorption refrigeration system cannot operate normally, i.e., the conventional single-effect absorption refrigeration circulation cannot utilize a heat source at a lower temperature to produce the cooling capacity at the required temperature. However, high-temperature and high-concentration lithium bromide solution may cause severe corrosion against common metal materials for absorption refrigeration systems, such as copper and carbon steel, etc. Consequently, efficient utilization of low-grade heat sources at 80° C. or lower temperatures by the H2O—LiBr working medium pair is limited.
A lithium bromide absorption refrigeration system is a refrigeration system that utilizes low-grade heat energy (residual heat, waste heat, etc.) as the driving power. Such a system saves electric power remarkably compared with a vapor compression refrigerator. If the temperature of the heat source can be decreased effectively, a wider range of heat sources will be provided for absorption refrigeration. To utilize heat at a lower temperature to produce the cooling capacity at a required refrigeration temperature, a two-stage absorption refrigeration system has been put forth. The working circulation of a two-stage absorption refrigeration system can produce cooling capacity at a lower temperature than the single-effect circulation, but the performance coefficient of such a working circulation is approximately half of the performance coefficient of the conventional single-effect circulation. Hence, it is an urgent task to decrease the temperature of the heat source for the system while maintaining a high performance coefficient of the system.
A conventional lithium bromide absorption refrigeration system can produce an evaporation temperature and cooling capacity of about 5° C., owing to the physical properties of lithium bromide. Lithium chloride cannot meet the requirement. However, the result of preliminary research has indicated that an absorption working medium pair composed of LiCl—H2O has higher thermodynamic performance. In the present invention, the temperature of the cold source is increased by changing the air conditioning mode, so that an absorption refrigeration circulation that utilizes LiCl—H2O as a working medium pair can be used for air conditioning, and thereby low-grade heat energy can be utilized efficiently, and the overall energy efficiency of the air conditioning system can be improved.
Liquid dehumidification-regeneration circulation systems have been widely applied in a variety of systems, owing to their advantages, such as low temperature of driving heat source, simple system structure, high energy storage density, and easy implementation, etc. In a liquid dehumidification-regeneration circulation system, the core components, including dehumidifier and regenerator, often exchange heat with air in a packed tower, and can bear the latent heat load in the system. Hence, the system is an energy-saving and environment-friendly circulation system.
It is seen from the above analysis: the two techniques are well complementary to each other. Therefore, it is of far reaching importance to make research on low-grade heat driven temperature and humidity separately processed air conditioning methods and systems.